We infer from the above that the dark current generation rate of the photodiode is high in the depletion region. How?
Generally in semiconductor the carrier generation and recombination will takes place.
Similarly the generation and regeneration mainly depends on transition.
And the distance between valence band and conduction band and the regeneration rate is -ve.
https://www.researchgate.net/publication/51455074_Comparison_of_photodiode_nonlinearity_measurement_systems
The depletion region has very low carrier concentration - any carrier to appear there is soon gone quickly drifting toward contacts. The recombination is proportional to product of concentration of holes and electrons because that indicates how often they can meet. So usually, there is very little recombination going on in the depletion region.
On another hand generation rate is typically independent of the carrier concentration, it is either thermal or light induced.
However, in forward biased diode the former depletion region of semiconductor becomes a place subjected to intense carrier injection and intensive recombination.
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